On airplanes, ailerons are movable control surfaces on the outboard rear sections of each wing, and are partly responsible for steering. They are usually located on the outside section of the wing, where they are most effective. They should not be confused with flaps, which are another set of movable surfaces on the wing, usually located inboard of each aileron. The flaps are generally not used for steering, but rather for providing lift at takeoff and landing.
The ailerons on the right and left sides of the plane are deflected in opposite directions, causing the entire plane to bank, or roll, in one direction or the other. For example, to bank right, the aileron on the right wing will go up, and the aileron on the left wing will go down at the same time. The disrupted airflow pattern will cause the plane to roll to the right. For steering purposes, aileron movements made in tandem with movements of the airplane's rudder, located on the tail. Also, stunt planes performing aerial acrobatic rolls use ailerons to literally roll completely around. Most aircraft are not meant for such extreme movements, as they can put considerable stress on the wings, possibly leading to structural failure.
In rare situations, ailerons can also be used to balance unusual forces on an aircraft. In cases, such as a single engine failure, or if there is a fuel leak on one wing, the aircraft may experience asymmetrical forces that must be stabilized. Certain wind conditions may also cause this kind of problem. A pair of very small movable surfaces, known as trim tabs, are located on each aileron. These tabs are normally kept neutral, but may be adjusted out of the neutral position if necessary. Thus, the trim tabs allow the pilot to change the neutral position of the ailerons themselves in order to counter any asymmetrical force, allowing the plane to continue on a straight course.
The ailerons are controlled using a couple of different methods. The yoke, the main control of the airplane that is in the pilot's hands, is one way to adjust them. They can also be controlled by the autopilot. Turning the heading knob to a different direction will automatically cause the ailerons to adjust in a way that will turn the plane in the desired direction. As the plane moves closer to that heading, they will then slowly begin to return to a neutral position, thus keeping the plane pointed in the direction requested.
Without properly working aileron surfaces, the steering of the plane becomes very difficult. In emergency situations, it may be necessary to steer the plane with the rudder alone. Steering may also be done, in a multiple engine aircraft, by applying asymmetrical power to the engines on one side or the other. The best way, however, to steer is with the ailerons on both wings as this provides the most control. These other methods should only be utilized under desperate circumstances.